Abstract The magnetomechanical behaviour of iron, nickel, gadolinium and terbium is reviewed and it is shown that the classification by Roberts and Barrand (1969) into iron-like or nickel-like materials is unsatisfactory. Magnetic damping is caused by the movement of 90° domain walls over internal stress barriers. Dislocations provide an obvious source of internal stress and a simple model of domain walls pinned by dislocations is used to develop a theory to explain the damping. The experimental values agree with the theory for gadolinium and terbium, and also for iron if a loss due to the interaction of interstitials with the domain walls is subtracted from the total damping. In the case of nickel good agreement with theory is obtained only when the fact that more than one type of Barkhausen jump contributes to the damping is considered.